Testing it out and so far I like it.
http://tanaya.net/DynaStop/
I'm going to see how it works. So far doing a modest test What I'm doing is a DEFER on the lowest MX record but no test on the next higher MX. The idea is that good email retries on the higher MX and goes through. Spam often doesn't retry and therefore a lot of (but not all) will not come back. If this works out I might do other blocks like Dynamic IP AND listed in blacklists that I normally don't trust enough to blacklist by itself.
